Psoriasis is a chronic skin disease affecting approximately 2-3% of the world population. Presently, psoriasis is without a permanent cure and its influence on the affected individual's life quality is devastating. People often experience flares and remissions throughout their life. Although new biological-immunological therapies are being developed, the mainstay armamentarium to treat psoriasis systemically includes methotrexate, cyclosporin and oral retinoids. Each treatment has advantages and disadvantages, and what works for one patient may not be effective for another.
Since the 1930s, vitamin A deficiency has been known to cause hyperkeratosis of the skin (phrynoderma) and as early as 1960s synthetic Vitamin A has been used for the treatment of psoriasis, though with low efficacy over toxicity ratio. Further research resulted in the development of the second generation of retinoids, the mono-aromatic retinoids, etretinate and its metabolite acitretin. Etretinate and acitretin are highly effective systemic treatments for psoriasis as well as for disorders of keratinization and for cutaneous lupus. However, despite the demonstrated clinical success of retinoid therapy, this treatment has a significant potential for toxicity, especially elevated liver functions and elevated triglycerides and LDL-Cholesterol and it requires close laboratory supervision. In addition, teratogenicity, the primary side-effect of retinoids, remains a major concern.
There are several forms of psoriasis, and each form has unique characteristics that allow dermatologists to visually identify psoriasis to determine what type, or types, of psoriasis is present. Sometimes a skin biopsy will be performed to confirm the diagnosis. The main types of psoriasis include the following:                Plaque Psoriasis (reddened areas a few inches across covered by silvery scales)        Pustular Psoriasis (blisters of noninfectious pus on red skin)        Arthritic Psoriasis or Psoriatic Arthritis        Guttate Psoriasis (small, red spots on the skin)        Inverse or Flexural Psoriasis (shiny, red patches in areas of friction such as in the folds of skin in the groin, the armpits or under the breasts)        Erythrodermic Psoriasis (reddening and scaling of most of the skin).        
Treatment depends on the severity and type of psoriasis. Some psoriasis is so mild that the person is unaware of the condition. A few develop such severe psoriasis that lesions cover most of the body and hospitalization is required. These represent the extremes. Most cases of psoriasis fall somewhere in between.
Psoriasis treatments fall into 3 categories:                Topical (applied to the skin)—Mild to moderate psoriasis        Phototherapy (light, usually ultraviolet, applied to the skin)—Moderate to severe psoriasis        Systemic (taken orally or by injection or infusion)—Moderate, severe or disabling psoriasis.        
Bollag, W. and Ott, F. (1999) Dermatology 199:308-312, describe the treatment of chronic hand eczema with oral 9-cis-retinoic acid. The article states that “Psoriasis . . . did not respond to well-tolerated doses of oral 9-cis-retinoic acid”.
Peter C. M. van de Kerkhof (2006) Dermatologic Therapy 19:252-263, describes the use of Acitretin (SORIATANE®, Roche Pharmaceuticals), a second generation oral systemic retinoid, for the treatment of psoriasis.